Bis(ethylenediammonium) μ-ethylenediaminetetraacetato-1κ3O,N,O′:2κ3O′′,N′,O′′′-bis[trioxidomolybdate(VI)] tetrahydrate

The title compound is a binuclear complex of molybdenum with a ethylenediaminetretraacetate ligand bridging two MoO3 units.

The single-crystal structure shows that the 2:1 Mo-edta complex anion of the title compound is discrete (Fig. 1).All of the carboxylic groups of H 4 edta are deprotonated, coordinating the molybdenum oxide groups by nitrogen and two oxygen atoms.The edta 4À ligand itself is a bridge between the two MoO 3 units, and the midpoint of the central C-C bond is situated on an inversion centre.In the 2:1 Mo-edta complex, the edta 4À ligand thus chelates a pair of Mo VI centres, in a tridentate fashion, giving a trans configuration to the complex.Each Mo VI ion is chelated by the edta 4À ligand, simultaneously forming two glycinato rings occupying contiguous vertices that define one face of the coordination polyhedron.The other three vertices of the opposite face are occupied by three terminal oxo atoms of the MoO 3 unit, completing the octahedral geometry.In the complex, the Mo-O bond lengths are in the range 1.7195 (16) to 1.7686 (15) A ˚for Mo O t groups (O t are terminal oxygen atoms: O5, O6 and O7).The resulting bond angles O t -Mo-O t are 107.27(7), 103.83 (7) and 106.75 (7) � , considerably larger than the expected value of 90 � for a regular octahedron, confirming the distortion from octahedral geometry.
The crystal packing can be rationalized in terms of nonbonding interactions between the three tectons: the Mo-edta complex anion, two (C 2 H 10 N 2 ) + cations and four lattice water molecules.These units are linked through hydrogen bonds of the type N-H� � �O water , N-H� � �O edta and O-H� � �O (Table 1).This interconnection leads to the supramolecular structure, as shown in Fig. 2.

Synthesis and crystallization
Solid molybdenum oxide (4 mmol) and ethylenediamine (4 mmol) were mixed in 30 ml of distilled water.To this data reports Figure 1 Molecular structure of the title compound with displacement ellipsoids drawn at the 50% probability level.Unlabelled atoms are generated by inversion symmetry.

Figure 2
Supramolecular arrangement of the title compound with hydrogen bonds shown as dotted lines.
mixture were slowly added 2 mmol of ethylenediamminetetraacetic acid (H 4 edta) under vigorous stirring.The solution was then stirred for 2 h at room temperature.The colourless solution thus obtained was left at room temperature for slow evaporation of water.After a few days, colourless crystals (yield 13.6% based on Mo) were obtained.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 2.

Table 2
Experimental details.